1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of fabricating a liquid crystal display device, and more particularly, to an in-plane switching mode liquid crystal display device and method of fabricating an in-plane switching liquid crystal display device.
2. Description of the Related Art
Presently, various portable electronic devices, such as mobile phones, PDAs, and notebook computers are being developed that require flat panel display devices. Liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, and vacuum fluorescent display (VFD) devices are actively being developed as flat panel display devices. Among these various devices, the LCD devices are appealing because of their mass production techniques, ease of driving, and implementation of high picture quality.
In the liquid crystal display device, there are various display modes according to arrangement of liquid crystal molecules of a liquid crystal layer. A Twisted Nematic (TN) mode is commonly used because of its simple display of black and white images, fast response time, and low driving voltage. In the TN-mode liquid crystal display device, liquid crystal molecules that are initially aligned along a horizontal direction to the substrate are subsequently aligned almost vertically to the substrate when a voltage is applied to the liquid crystal layer. Accordingly, viewing angle becomes narrow due to a refractive anisotropy of the liquid crystal molecules when the voltage is applied.
To solve the viewing angle problem, there have been proposed LCD devices with various display modes having wide viewing angle characteristics. Of the LCD devices, an in-plane switching (IPS) mode liquid crystal display device has been adopted in which at least a pair of electrodes are arranged in parallel within a pixel region to form a horizontal electric field substantially parallel to the surface of a substrate, thereby aligning liquid crystal molecules within a single plane.
FIG. 1A is a plan view of an in-plane switching mode LCD device according to the related art, and FIG. 1B is a cross sectional view along I-I′ of FIG. 1A according to the related art. In FIG. 1A, a pixel of a liquid crystal display panel 1 is defined by a gate line 3 and a data line 4 arranged along longitudinal and transverse directions. Although FIG. 1A only shows an (n,m)th pixel, an N (>n) number of gate lines 3 and an M (>m) number of data lines 4 are arranged on the liquid crystal display panel 1 to form an N×M matrix of pixels. A thin film transistor 10 is formed at a crossing region of the gate line 3 and the data line 4 within the pixel region. The thin film transistor 10 includes a gate electrode 11 to which a scan signal is supplied from the gate line 3, a semiconductor layer 12 formed on the gate electrode 11 and activated as the scan signal is supplied to form a channel layer, and a source electrode 13 and a drain electrode 14 to which an image signal is supplied through the data line 4 and formed on the semiconductor layer 13 in order to supply an image signal input from an outer side to a liquid crystal layer.
A plurality of common electrodes 5 and pixel electrodes 7 are arranged to be parallel with the data line 4 within the pixel region. In addition, a common line 16 connected to the common electrode 5 is disposed on a center portion of the pixel region, and a pixel electrode line 18 connected to the pixel electrode 7 is disposed on the common line 16 to overlap with each other. A storage capacitance is formed by the overlap of the common line 16 and the pixel electrode line 18 in the IPS-mode LCD device.
Accordingly, in the IPS-mode LCD device, the liquid crystal molecules are oriented to be parallel with the common electrode 5 and the pixel electrode 7. When a signal is supplied to the pixel electrode 7 by operation of the thin film transistor 10, a horizontal electric field parallel with a surface of the liquid crystal display panel 1 is generated between the common electrode 5 and the pixel electrode 7. Accordingly, the liquid crystal molecules are rotated along a same plane with the horizontal electric field. Thus, grey inversion due to the refractive anisotropy of the liquid crystal molecules can be prevented.
In FIG. 1B, the gate electrode 11 is formed on the first substrate 20, and a gate insulating layer 22 is deposited on an entire surface of the first substrate 20. A semiconductor layer 12 is formed on the gate insulating layer 22, and the source electrode 13 and the drain electrode 14 are formed thereon. In addition, a passivation layer 24 is formed on an entire surface of the first substrate 20. A plurality of common electrodes 5 are formed on the first substrate 20, and the pixel electrode 7 and the data line 4 are formed on the gate insulating layer 22. Accordingly, the horizontal electric field is generated between the common electrode 5 and the pixel electrode 7.
A black matrix 32 and a color filter layer 34 are formed on a second substrate 30. The black matrix 32 prevents light from leaking toward an area where alignment of the liquid crystal molecules are not controlled by the electric field, and is formed mainly on an area of the thin film transistor 10 between adjacent pixels (i.e., the gate line and the data line areas). The color filter layer 34 includes red (R), green (G), and blue (B) sub-color filters for generating colored images, and a liquid crystal layer 40 is formed between the first substrate 20 and the second substrate 30.
Operating methods of the IPS-mode LCD device can be classified into one of three different inversion methods in accordance with a phase of the data voltage that is supplied to the data line. These methods include a line inversion method, a column inversion method, and a dot inversion method. The line inversion method inverts the phase of the data voltage supplied to the data line 4 according to the gate signal supplied to the gate line 3. The column inversion method inverts the phase of the data voltage supplied to the data line 4 at every column. The dot inversion method inverts the phase of polarity of the voltage supplied to the data line 4 at every column and line simultaneously. The phase of the data voltage is inverted and supplied to the data line in order to prevent generation of cross-talk on a display screen due to degradation of the liquid crystal material when the same voltage is continuously supplied between adjacent pixel and common electrodes.
However, using the dot inversion method in the IPS-mode LCD device is problematic. For example, as shown in FIG. 1A, one common voltage is supplied to one pixel such that a positive voltage and a negative voltage of the data voltage should be repeated at every frame for the dot inversion operation. Accordingly, when the data voltage is changed from the positive to the negative, a variation is generated on the common electrode by the voltage difference of the data voltage, and the variation causes generating flicker of the displayed image, residual image, or a horizontal dim.